Within the 3rd Generation Partnership Project (3GPP), the design and specification of the next generation of wireless communications networks is ongoing in an effort known as the Long Term Evolution (LTE) initiative. Along with the definition of new wireless interfaces, a new core network architecture is also being defined. This definition is known as System Architecture Evolution (SAE). As shown in FIG. 1, an LTE/SAE network includes two types of network elements supporting user and control planes: an enhanced base station 110, called the Evolved NodeB or “eNodeB”; and the Access Gateway (aGW) 120. The eNodeB 110 provides the LTE air interface and radio resource management, while the AGW provides a mobility anchor point for the user plane and provides a gateway to IP Service Networks 140, which may include the Internet, intranets, and other IP-based service networks.
Until recently, discussions regarding LTE mobility, i.e., handover from one eNodeB 110 to another, have been based on the assumption that the Packet Data Convergence Protocol (PDCP) is terminated in the LTE Access Gateway node 120 at one end and in the user equipment (UE) 160 at the other. PDCP, part of Layer 2, performs IP header compression and decompression, as well as ciphering and integrity protection of transmitted data. PDCP sequence numbers are added to user data, primarily for ciphering purposes; these sequence numbers may be used in handover procedures for reordering of packets and detection of duplicate packets. FIG. 2A thus illustrates the prior understanding of the allocation of Layer 1 and Layer 2 functionality between the UE 100, the evolved NodeB (eNodeB) 110, and the aGW 120. As shown in FIG. 2A, PDCP terminates in aGW 120, while the Radio Link Control (RLC) and Medium Access Control protocols terminate in the eNodeB 110.
Those skilled in the art will appreciate that a typical handover procedure in a system utilizing the architecture depicted in FIG. 2A need not involve the PDCP, because an inter-eNodeB 110 handover does not require a change in aGW 120. One advantage of this architecture is that header compression can continue through a handover process without being restarted or moved to another node in the radio access network or in the core network. This applies to both uplink and downlink data transfers.
Recently, however, 3GPP has decided to locate the PDCP functionality in the eNodeB, rather than in the aGW, as shown in FIG. 2B. The move of PDCP functionality to the eNodeB has several implications for mobility. For instance, the header compression functionality in the PDCP “moves” from the source eNodeB 110 to the target eNodeB 110 during handover.
Header compression requires flow classification—the header of each incoming IP packet must be inspected in order for the compressor to identify the flow to which the packet belongs, and the corresponding compression state to use. When multiple IP flows with varying service requirements share the same PDCP instance, it is then possible to identify and distinguish between IP packets based on their service requirements at the eNodeB 110. For example, different IP flows may have different requirements with respect to avoidance of duplicate packets, loss of packets, in-sequence delivery, interruption time, and/or jitter.